260 PRACTICAL ORGANIC CHEMISTRY
saturated compound, forms additive compounds with halogens
and halogen acids. With permanganate solution it may be
converted into glycerol,
CH2:CH.CHoOH + H\jO -\- O = CH2OH.CHOH.CH.jOH.
On oxidation with silver oxide it yields the corresponding alde-
hyde (acrolein) and the acid (acrylic acid).
Isopropyl Iodide.—The replacement of hydroxyl by iodine
in the action of phosphorus and iodine on alcohols has already
been described (see Prep. 6, p. 68), but here the presence of an
excess of hydriodic acid, which is due to the action of water on
the phosphorus iodide,
PI8 -h 3H,0 = P(OH)3 + 3HI,
exerts in addition a reducing action on certain of the hydroxyl
groups. By diminishing the proportion of phosphorus and
iodine to glycerol, the reaction may be interrupted at an earlier
stage, when ally! iodide is formed. This is probably due to the
splitting off of iodine from propenyl tri-iodide,
CILJ.CIILCIU = CH2:CH.CH.J + I3,
On the other hand a larger proportion of phosphorus and iodine
or cone, hydriodic acid will reduce allyl iodide to propylene,
CII3:CM.CHaI -1- HI = CH2:CII.CH, + L,.
The action of hydriodic acid on glycerol is typical of the
polyhydric alcohols. Hydriodic acid converts erythritol into
secondary butyl iodide, and mannitol into secondary hexyl
iodide. The normal iodides are never formed.
Bpichlorhydrin.—It is a noteworthy fact that althoug-h
hydrochloric acid can replace hydroxyl by chlorine in the case
-of the monohydric alcohols, the number of hydroxyl groups wliich
are substituted in the case of polyhydric alcohols is strictly
limited. Like glycerol, ethylene glycol gives a chlorhydrin,
CHoOH.CHoOH -1- IIC1 = CH-oOH.CHoCl + I-IflO.